The effect of coke lay-down on n-heptane reforming on Pt and Pt-Sn catalysts

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In this paper, we report detailed studies regarding the reforming of n-heptane and related molecules carried out under near-industrial conditions on supported Pt and Pt-Sn catalysts of the type used in industry. We have correlated the performance of these catalysts with the level of coke laid down on the surface measured by TGA. The results indicate that the presence of coke reduces hydrogenolysis/cracking and favours aromatisation. The presence of tin in the catalyst produces much faster coke lay-down, and, in turn, this gives higher selectivity to the desired products in a much shorter time on stream. The initial rate of coke lay-down is very rapid, but it slows to a near-zero rate after this initial period, when 2% of the catalyst weight of carbon has been deposited on the surface; we propose that this is a near-monolayer passivating layer which promotes toluene production. The presence of chlorine on the support increases the activity, the cracking and the coking. Consideration is given to the nature of the species responsible for the coking of the catalyst.